This invention generally relates to valve mounting assemblies for aerosol containers, said mounting assemblies being commonly referred to as "mounting cups." More particularly, this invention relates to an improved gasket for the mounting cup, i.e., the gasket that forms the seal between the perimetal rim of the mounting cup and the bead of the aerosol container, wherein the sleeve gasket is folded over an itself to provide a double thickness of gasket material disposed within the channel portion of the mounting cup. Also, the invention relates to a method and apparatus for forming the folded-over gasket after the gasket material has been disposed on the mounting cup.
Aerosol containers are widely used to package a variety of fluid materials, both liquid and powdered particulate products. Typically, the product and a propellant are confined within the container, at above atmospheric pressure, and the product is released from the container by manually opening a dispensing valve to cause the pressure within the container to deliver the product through the valve and connecting conduits to a discharge orifice.
The dispensing valve, crimped to a mounting cup having a sealing gasket, is normally mounted in a top opening of the container, which opening is defined by a component commonly referred to as the "bead" of the container opening. The mounting cup includes a central pedestal portion for crimping the dispensing valve, a profile portion extending outward from the pedestal portion, which profile portion merges into an upwardly extending body portion, the body portion emerging into a hemispherically-shaped channel portion terminating in a skirt portion, which channel is configured to receive the bead portion of the container opening. The sealing gasket normally is disposed within the channel portion and in many gasket configurations extends downward along a part of the body portion. After the sealing gasket is disposed onto the mounting cup, the cup is positioned onto the container and the cup is clinched to the container. The clinching operation is well-known to those skilled in the aerosol container art.
In an aerosol container, an effective seal between the mounting cup and the container bead is obviously critical. This seal is accomplished through the sealing gasket, which must prevent the loss of pressure (propellant) through the interface between the container bead and mounting cup.
Various types of sealing gaskets are known in the art. One common type of gasket comprises a conventional flat rubber gasket that is placed inside the channel of the mounting cup. Gaskets of this type are typically manufactured by extruding, molding and vulcanizing the compounded rubber mixture onto rods and then cutting or slicing off thin, annular sections of the extruded and vulcanized product (tube). These gaskets are often referred to as cut or flat gaskets. Cut gaskets are relatively expensive to manufacture. It is very difficult to control precisely the radial dimensions of the tubes, from which the cut gaskets are made, the tubes having varying dimensions and being out of round. Consequently, the outer cylindrical surfaces of these tubes are usually machined to the desired dimensions, said matching adding considerable cost to the gasket manufacture.
Another type of gasket comprises a relatively thin sleeve of elastomeric material that is mounted on the body portion of the mounting cup and then advanced along said body so that the gasket extends ultimately into a limited portion of the annular channel of the mounting cup as well as downward along the body portion beyond the annular clinch zone. When the mounting cup is mounted and then clinched onto the aerosol container, the sealing gasket is forced into a sealing engagement with both the channel of the mounting cup and the bead of the container. Typically, these gaskets are forced into a sealing engagement with the mounting cup along only a relatively small circumferential portion of the gasket at positions referred to as the 5 o'clock and 11 o'clock positions. Due to their shape, gaskets of this type are often referred to as sleeve gaskets.
Sleeve gaskets are manufactured by advancing a tube of gasket material onto the body of the mounting cup and then cutting or slicing off annular sections of the tube. The axial heights of sleeve gaskets, however, are substantially greater than the axial heights of cut gasket. Sleeve gaskets are much less expensive to make and assemble to the mounting cup than cut gaskets. When making sleeve gaskets, it is not necessary to machine the outside cylindrical surface of the extruded tubes of gasket material. Moreover, a tubular sleeve gasket may be assembled to the mounting cup more easily than assembling a cut gasket to the mounting cup.
The sealing gasket may also be formed by a liquid material containing water or solvent that is deposited on the annular channel and body portion of the mounting cup. The solvent or water evaporate during curing and the remaining material produces a resilient sealing material in the mounting cup channel. Forming the gasket from a liquid material also is a comparatively expensive procedure requiring multiple production steps including the use of curing ovens or other means to dry and cure the gasket material. Moreover, means must be provided for rotating the mounting cup beneath and relative to a metering apparatus that dispenses carefully determined amounts of a gasket forming composition. These gaskets are commonly referred to as "flowed-in" gaskets. The "flowed-in" gasket system has been disfavored recently due to environmental concerns.
Thus, the above described types of gaskets, as well as others that may be used, have both advantages and disadvantages. Both cut and sleeve gaskets generally produce excellent sealing results. Cut gaskets have seen widespread commercial use for a longer period of time than sleeve gaskets. When using sleeve gaskets on filling and clinching equipment previously used with flat or cut gaskets, a time consuming adjustment is necessary to the clinching tool. Often, a clinching line will be required to accommodate both flat and sleeve gaskets, depending on the gasket specifications of the valved container being clinched. To avoid having to make the clinching tool adjustment, and the consequent down-time, there has been a tendency, particularly in Europe, to stay with flat or cut gaskets, even though such gaskets are more costly.
In the past, an attempt has been made to overcome the disadvantages of a cut gasket by converting a specially dimensioned sleeve-type gasket into a cut-type gasket. This attempt is described in U.S. patent application Ser. No. 08/384,736, filed on Feb. 3, 1995, now abandoned. A disadvantage of utilizing the aforementioned sleeve to cut-type gasket is that the apparatus used to manufacture the sleeve-type gasket is designed to handle tubing having a thickness on the order of 0.014". Cut gaskets generally are 0.040" thick, and to manufacture sleeve-type gasket material for conversion into a cut-type gasket of 0.040" or more requires a significant retooling.